Soybean seeds represent perhaps the most significant oilseed in the world. Soybean oil makes up approximately 28% of the world supply of fats and oils, has been considered to be the major vegetable oil produced and consumed in the United States, and more than 90% of the soybean oil is used in food products (World Soybean Research Conference III Proceeding, Shibles, R. (Ed.) 1985).
Soybeans thus represent a significant world-wide food source, providing an excellent source of protein. As such, soybeans represent potential alternatives to meats.
Tofu and soymilk are two principal food products derived from soybean seeds. More than one billion people in China and Southeast Asia, it has been stated, rely on tofu as a major food protein source. (Proc. Int. Soya Protein Food Conf., American Soybean Assoc., p. 35 (1970)). Soymilk is similarly an important source for food protein.
One application for which soybean oil may be used is the production of plastic fats (e.g.--shortenings and margarines). Such plastic fats are made with a matrix of solid fats whose interstices are filled with liquid oil. Solid fats can crystallize in several forms with different melting points and physical properties. The forms are commonly designated alpha, beta' and beta, with the beta form having the highest melting point and the greatest stability. Forms other than these three may also be present. The beta' form generally has the properties that are most usually desired in a plastic fat.
If the solid portion of the plastic fat contains about 15% or more of palmitic acid and the rest is stearic acid, it will stabilize in the beta' form. If the ratio of stearic/palmitic is higher, then the fat may convert to the beta form with its less desirable physical structure.
Soybean oil will most usually contain a level of about 10% palmitic acid or so. Accordingly, if such soybean oil is hydrogenated and made into a plastic fat, it will likely crystallize in the beta form. To prevent this, an oil such as cottonseed or palm oil that is richer in palmitic acid is blended with the soybean oil.
The use of either palm oil or cottonseed oil presents some difficulties. Some users thus consider palm oil to be undesirable based upon perceived health considerations. On the other hand, cottonseed oil is generally available only in limited amounts at a higher price than that of soybean oil. It would accordingly be highly desirable to be able to provide soybean varieties having sufficiently elevated palmitic acid contents so that plastic fats can be produced such that such products will stabilize in the beta' form.
Further, some producers for some plastic fat applications believe that soybean oil having a palmitic acid content in the range of about 13% or 14% to about 16% or so is preferred. For such applications, it would be highly desirable to be able to provide soybean varieties having a sufficiently high level of palmitic acid to use for blending with soybean varieties having more conventional palmitic acid contents to provide the desired intermediate range of palmitic acid content.
The palmitic acid levels in soybean seed oil range from 9.3% to 17.4% within the world collection (Erickson et al., Journal of Heredity, 79, p. 465, 1988). The Erickson et al. article reports the inheritance of altered palmitic acid percentages in two soybean mutants, C1726 and C1727. The level of palmitic acid in C1727 reported averages 17.3% palmitic acid in comparison to 11.5% in the oil of the parent cultivar "Century."
Despite the clear need for soybeans having a level of palmitic acid above that present in the world collection at the present time, this objective still remains to be achieved.